RNAi based therapeutics offers great promise for a myriad of diseases. The Kay laboratory has successfully used an AAV vector-based approach to express shRNAs from liver. We have established that such vectors can safely and persistently reduce Hepatitis B viral (HBV) replication by 2 to 3 logs in HBV transgenic mice. Nonetheless, we have established that over expression of some shRNAs can result in fatality due to liver failure. Liver failure was associated with interference in the endogenous microRNA processing pathway and at least part of the block was at the level of Exportin-5. The Rossi laboratory has developed alternative shRNA expression strategies some of which bypass the Exportin-5 pathway. The two labs together offer a synergistic approach such that in the proposed consortium, they will work together to further unravel the mechanisms involved in shRNA based toxicities as well as develop new expression paradigms for in vivo shRNA based therapeutics.